Add unique id for each worker and pass it to the child process

CHANGELOG.md

@@ -1,5 +1,11 @@
 ## master
 
+### Features
+
+* `[jest-worker]` Assign a unique id for each worker and pass it to the child
+  process. It will be available via `process.env.JEST_WORKER_ID`
+  ([#5494](https://github.com/facebook/jest/pull/5494))
+
 ## jest 22.2.1
 
 ### Fixes

packages/jest-worker/README.md

@@ -130,6 +130,9 @@ overriding options through `forkOptions`.
 Finishes the workers by killing all workers. No further calls can be done to the
 `Worker` instance.
 
+**Note:** Each worker has a unique id (index that starts with `1`) which is
+available on `process.env.JEST_WORKER_ID`
+
 # More examples
 
 ## Standard usage
@@ -143,12 +146,13 @@ import Worker from 'jest-worker';
 
 async function main() {
   const myWorker = new Worker(require.resolve('./worker'), {
-    exposedMethods: ['foo', 'bar'],
+    exposedMethods: ['foo', 'bar', 'getWorkerId'],
     numWorkers: 4,
   });
 
   console.log(await myWorker.foo('Alice')); // "Hello from foo: Alice"
   console.log(await myWorker.bar('Bob')); // "Hello from bar: Bob"
+  console.log(await myWorker.getWorkerId()); // "3" -> this message has sent from the 3rd worker
 
   myWorker.end();
 }
@@ -166,6 +170,10 @@ export function foo(param) {
 export function bar(param) {
   return 'Hello from bar: ' + param;
 }
+
+export function getWorkerId() {
+  return process.env.JEST_WORKER_ID;
+}
 ```
 
 ## Bound worker usage:

packages/jest-worker/src/__tests__/index.test.js

@@ -122,10 +122,26 @@ it('tries instantiating workers with the right options', () => {
   expect(Worker.mock.calls[0][0]).toEqual({
     forkOptions: {execArgv: []},
     maxRetries: 6,
+    workerId: 1,
     workerPath: '/tmp/baz.js',
   });
 });
 
+it('create multiple workers with unique worker ids', () => {
+  // eslint-disable-next-line no-new
+  new Farm('/tmp/baz.js', {
+    exposedMethods: ['foo', 'bar'],
+    forkOptions: {execArgv: []},
+    maxRetries: 6,
+    numWorkers: 3,
+  });
+
+  expect(Worker).toHaveBeenCalledTimes(3);
+  expect(Worker.mock.calls[0][0].workerId).toEqual(1);
+  expect(Worker.mock.calls[1][0].workerId).toEqual(2);
+  expect(Worker.mock.calls[2][0].workerId).toEqual(3);
+});
+
 it('makes a non-existing relative worker throw', () => {
   expect(
     () =>

packages/jest-worker/src/__tests__/worker.test.js

@@ -57,6 +57,7 @@ it('passes fork options down to child_process.fork, adding the defaults', () =>
       execPath: 'hello',
     },
     maxRetries: 3,
+    workerId: process.env.JEST_WORKER_ID,
     workerPath: '/tmp/foo/bar/baz.js',
   });
 
@@ -70,6 +71,17 @@ it('passes fork options down to child_process.fork, adding the defaults', () =>
   });
 });
 
+it('passes workerId to the child process and assign it to env.JEST_WORKER_ID', () => {
+  new Worker({
+    forkOptions: {},
+    maxRetries: 3,
+    workerId: 2,
+    workerPath: '/tmp/foo',
+  });
+
+  expect(childProcess.fork.mock.calls[0][1].env.JEST_WORKER_ID).toEqual(2);
+});
+
 it('initializes the child process with the given workerPath', () => {
   new Worker({
     forkOptions: {},

packages/jest-worker/src/index.js

@@ -66,14 +66,16 @@ export default class {
       workerPath = require.resolve(workerPath);
     }
 
-    // Build the options once for all workers to avoid allocating extra objects.
-    const workerOptions = {
+    const sharedWorkerOptions = {
       forkOptions: options.forkOptions || {},
       maxRetries: options.maxRetries || 3,
       workerPath,
     };
 
     for (let i = 0; i < numWorkers; i++) {
+      const workerOptions = Object.assign({}, sharedWorkerOptions, {
+        workerId: i + 1,
+      });
       const worker = new Worker(workerOptions);
       const workerStdout = worker.getStdout();
       const workerStderr = worker.getStderr();

packages/jest-worker/src/types.js

@@ -46,6 +46,7 @@ export type FarmOptions = {
 export type WorkerOptions = {|
   forkOptions: ForkOptions,
   maxRetries: number,
+  workerId: number,
   workerPath: string,
 |};
 

packages/jest-worker/src/worker.js

@@ -79,7 +79,9 @@ export default class {
       Object.assign(
         {
           cwd: process.cwd(),
-          env: process.env,
+          env: Object.assign({}, process.env, {
+            JEST_WORKER_ID: this._options.workerId,
+          }),
           // suppress --debug / --inspect flags while preserving others (like --harmony)
           execArgv: process.execArgv.filter(v => !/^--(debug|inspect)/.test(v)),
           silent: true,